New observations of HF-induced optical emissions from the ionospheric E region

Details New observations of HF-induced optical emissions from the ionospheric E region New observations of HF-induced optical emissions from the ionospheric E region

Jun 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009jgra..11406316p&link_type=abstract

Journal of Geophysical Research, Volume 114, Issue A6, CiteID A06316

Physics

Ionosphere: Active Experiments, Atmospheric Composition And Structure: Airglow And Aurora, Ionosphere: Ionospheric Irregularities, Ionosphere: Auroral Ionosphere (2704), Radio Science: Ionospheric Propagation (0689, 2487, 3285, 4275, 4455)

Scientific paper

A new independent instance of highly localized artificial 557.7 nm optical emissions induced by high-power HF waves incident upon a precipitation-produced E layer at High Frequency Active Auroral Research Program (HAARP) confirms the original discovery of this phenomenon and adds a number of new observational facts. The features are excited by O mode transmissions but not X mode transmissions and disappear entirely during deliberate off periods. The specific transmitter pulsing period does not appear to be a critical factor, ruling out ULF resonances as a possible mechanism. The observed locations of the enhanced emissions are consistent with a small number of long-lived inhomogeneities traveling steadily across the field of view over several minutes. These persistent regions are preferentially excited even at a small fraction of peak power well away from the beam center and can reappear along the same trajectory after gaps of more than 1 min. The absence of any detectable enhancements in directly coincident 630.0 nm data or side-looking 557.7 and 630.0 nm images focused on the F region portion of the field line conclusively locates these artificial emissions in the ionospheric E region. We suggest possible hypotheses that might explain the new observations and the earlier results.

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